Blow molding is a fabrication method for hollow thermoplastic shapes. There are two general classes of plastic products made using the blow-molding process and related machinery: packaging products and technical parts. Packaging products include such items as bottles, jars, jugs, cans, and other containers. Technical parts include automotive components such as bumpers, fuel tanks, functional fluid containers, ducting, and the like. The term “articles” is used to encompass either or both packaging products and technical parts.
The blow-molding process can be of two general types: extrusion blow molding and injection blow molding. In extrusion blow molding, a thermoplastic parison is lowered from an extruder and between mold halves. The mold halves close around the parison, and the parison is then expanded against a mold cavity by introduction of a blowing gas, usually air. In injection molding, a thermoplastic material is first injection molded into a preform parison which is then transferred to a blow mold and expanded in the same manner as in an extrusion blow-molding process.
In intermittent extrusion, the molds are mounted to a common platen and the parisons are extruded by either a reciprocating screw extruder or by a ram accumulator which holds in readiness a volume of molten plastic material needed to make the next article or articles. In continuous extrusion, a molten parison is produced from an extruder die without interruption, and a segment of the parison is severed and positioned into a mold. The molds can be moved from station to station on rotating vertical wheels, on a rotating horizontal table, or with a reciprocating action. When the parison is extruded, the mold is moved under the extruder die or flow head to receive the parison segment and then is moved to a blowing station.
The positioning of the parison relative to the mold in a rotary system is relatively difficult. Therefore, many of the current blow-molding machines use the reciprocating mold concept according to which the molds are shuttled back and forth from station to station. A major drawback of the reciprocating mold concept, however, is a limitation on production rate.
A. Horizontal Rotary Blow-Molding Machines
Horizontal rotary blow-molding machines allow for high production rates of uniform articles. Such machines index circumferentially spaced mold halves in steps around a vertical axis. The mold halves each capture a vertical, continuously growing parison at an extrusion station. In one machine, the flow head extruding the parison moves up away from the mold halves after the mold halves close to capture the parison. The parison is severed adjacent the top of the mold halves, the mold halves are moved away from the extrusion station, and a top blow pin is moved into the end of the captured parison at the top of the mold halves to seal the mold cavity and blow the parison. Subsequently, the flow head and dependent parison are lowered back to the initial position so that the new parison is in position to be captured by the next pair of mold halves. The blown parison cools as the mold halves are rotated around the machine, following which the mold halves open at an ejection station and the finished article is ejected from between the mold halves. The machine includes an in-mold labeling station between the ejection station and the extrusion station for applying labels to the interior surfaces of the mold cavities.
In another horizontal rotary blow-molding machine the parison grows down over a blow pin at the bottom of the mold halves before closing of the mold halves. The flow head is moved up above the closed mold before severing of the new parison from the captured parison. The mold is then indexed laterally to the next station without dropping and the captured parison is blown within the cavity. In a further horizontal rotary blow-molding machine, the whole turntable supporting all of the mold halves is raised and lowered during rotation as each mold captures a parison at the extrusion station.
B. Utilities
Utilities such as chilled water, HVAC (heating, ventilation, and air conditioning), dehumidified air, and compressed air must be provided to the blow-molding machines. The chilled water is used to cool the molds. The chiller used to generate the chilled water must be located remote from the blow-molding machines given its heat load. The HVAC and dehumidified air are used to condition the space in which the blow-molding machines operate. More specifically, the dehumidified air conditions the environment of the blow-molding machine to prevent condensation on the molds (which, among other problems, can cause corrosion of the molds). A heat exchanger is provided to reduce the temperature of the air provided to the dehumidifier from ambient (about 20° C.) to about 10° C. An air compressor system provides compressed air needed to operate the machines.
Conventionally, the chiller, its related pump, the HVAC unit, the dehumidifier, its related heat exchanger, and the air compressor are all independent and isolated units. These six independent units require both substantial space (i.e., they create a large footprint) and mechanical connections (e.g., pipes, hoses, and the like). The time and cost involved with installing these individual components is substantial. In addition, the related cost of the components themselves, including the cost of connections to and from the components, is high.
To overcome the shortcomings of conventional systems that provide utilities to blow-molding machines for blow-molding articles, a new system having a multi-functional utility skid is provided for use with an air compressor and a chiller. In view of the relatively large commercial demand for various types of plastic articles, it would be desirable to reduce the cost of supplying utilities to blow-molding machines. The present invention satisfies this desire.
An object of the present invention is to reduce capital costs and installation costs. Related objects are to eliminate redundant components (such as a heat exchanger) and reduce the number and length of connections between, and the installation time of, the various components that comprise the system. Another object is to combine three components into one, reducing the footprint of the system and permitting the components to be located proximate (i.e., adjacent to) the blow-molding machine with minimal connections.